The Study Of Radiation Characteristics Of Thermo-chemical Nonequilibrium Flow Field Using State-to-State Model

In this paper,with the consideration of vibrational relaxation,chemical reaction and radiation transition,the state-to-state model is used to study the thermochemical and radiative nonequilibrium processes of O₂/O gas mixture,by simulating the closed stationary system as well as the one-dimensional flow field behind a positive shock wave.The quasiclassical trajectory method(QCT)and the forced harmonic oscillator model(FHO)are used to calculate the rate coefficients of the vibrational transitions and dissociation-recombination reactions of O₂ molecules through the collisions with O2molecules and O atoms.The calculated results are in good agreement with the results in references.Through these rate coefficients,the thermal chemical non-equilibrium process of the closed stationary system at constant volume and temperature is numerically simulated.Comparing with reference,the correctness of the model and calculation method are verified.Firstly,three micro reaction mechanisms controlling the vibration relaxation process(vibrational-translational energy exchange by collisions with molecule oxygen(VTm),vibrational-translational energy exchange by collisions with atom oxygen(VTa),and vibrational-vibrational energy exchange(VV))are considered separately to study the contribution of different mechanisms to the evolution of composition and energy level distribution.The results show that the vibrational-translational energy exchange plays a critical role in vibrational relaxation,which makes the vibrational distribution tend to the Boltzmann distribution at translational temperature,while the vibrational-vibrational energy exchange inhibits this process.Then,the vibrational relaxation and chemical reaction are calculated separately to study their interaction characteristics.The result shows that when the temperature is low,the characteristic time of chemical reaction is much longer than the relaxation time,which explain the reason why the chemical reaction process has a weak influence on the vibration relaxation process.Otherwise,when the temperature is high(T>10000K),both of them occur at the same time,and the chemical reaction has a great influence on the vibration relaxation process,which may make the vibration temperature present a non-monotonic change.Furthermore,the radiation transition is included in the nonequilibrium process,which is solved by coupling with vibration relaxation and chemical reaction.The evolution of nonequilibrium radiation coefficient and radiation intensity,as well as the contribution of each process to the chemical composition and vibration energy level distribution of the system are studied.The results show that the wavelength corresponding to the peak of spectral emission coefficient decreases with the increase of vibration temperature,while the wavelength corresponding to the peak of absorption coefficient increases with the increase of vibration temperature.the radiation generation term of molecular energy level is much smaller than that of translational-vibrational transition,and the characteristic time of non-equilibrium radiation is much longer than that of vibrational relaxation.Finally,the state-to-state model coupled with radiation is used to simulate the flow field behind a positive shock wave.The results show that the vibrational distribution deviates from the Boltzmann distribution at the vibrational temperature,two temperature model can't describe the vibrational distribution in detail.The larger the Mach number of the incoming flow is,the larger the peak value of the radiation intensity and the divergence term of the radiation heat flow after the shock wave is,and the shorter the time to reach the equilibrium radiation is.The influence of radiation on the nonequilibrium distribution of the field and the vibrational distribution is very small.